1. Field of the Invention
The present invention relates to an automatic transmission in the form of a belt-driven conical-pulley transmission, as it is known from, for example, DE 10 2004 015 215 and other publications, as well as to a method for manufacturing it, and to a vehicle equipped with it.
2. Description of the Related Art
In a broader sense, automatic transmissions are essentially modulating converters that stepwise or steplessly independently change the present transmission ratio as a function of current or expected operating conditions, such as partial load, thrust, and ambient parameters such as temperature, air pressure, and humidity. Included in that group are modulating converters that are based on electric, pneumatic, hydrodynamic, or hydrostatic principles, or a combination of those principles.
The automation relates to a diverse array of functions such as, for example, starting, transmission ratio selection, and type of transmission ratio change at various operation conditions, wherein the type of transmission ratio change can be understood as, for example, the shifting from one gear to another, the skipping of gears, and the speed of the shift.
The desire for comfort, reliability, and commercially acceptable manufacturing complexity and cost determines the degree of automation, in other words, how many functions run independently.
As a rule, the driver can manually engage the automatic process or restrict it to individual functions.
Automatic transmissions in a stricter sense, as they are used today especially in vehicle construction, generally have the following design:
Located on the input side of the transmission is a starting unit in the form of a controllable clutch, for example a wet or dry friction clutch, a hydrodynamic clutch, or a hydrodynamic converter.
A lockup clutch is frequently attached to a hydrodynamic converter in parallel to the pump and turbine portion, which increases efficiency through direct power transmission and dampens vibrations at critical rotational speeds through defined slippage.
The starting unit drives a mechanical, stepless or stepwise adjustable speed change transmission that can contain a forward-/reverse driving unit, a main-, range-, split group, and/or a variable speed drive unit. Gear groups are designed, according to requirements for smoothness of operation, space conditions, and transmission options, as reduction gearing or planetary arrangements with straight or diagonal teeth.
The output element of the mechanical transmission, a shaft or a gear, directly or indirectly drives a differential, via intermediate shafts or an intermediate step with a constant transmission ratio, which differential can be designed either as a separate transmission or as an integral component of the automatic transmission. In principle, the transmission is best suited for longitudinal or transverse installation in a motor vehicle.
Hydrostatic, pneumatic and/or electrical actuators are provided for adjusting the transmission ratio in the mechanical transmission. A hydraulic pump based on the principle of displacement delivers pressurized oil to the starting unit, in particular the hydrodynamic unit, for the hydrostatic actuators of the mechanical transmission and for the lubrication and cooling of the system. Gear pumps, screw type pumps, vane pumps, and piston pumps, with the latter mostly being of radial design, are used according to required pressure and displacement volume. In practice, gear pumps and radial piston pumps have proven themselves for that purpose, wherein the advantage of the gear pumps is that they are easy to manufacture, while the advantage of the radial piston pumps is their higher pressure level and their superior controllability.
The hydraulic pump can be provided at any desired site on the transmission on a main or an auxiliary shaft that is constantly driven by the drive unit.
Continuous automatic transmissions are known that include a drive unit, a planetary reverse gear as a forward-/reverse driving unit, a hydraulic pump, a variable speed drive unit, an intermediate shaft and a differential. The variable speed drive unit in turn includes two conical disk pairs and an endless torque-transmitting means. Each conical disk pair includes a second, axially displaceable conical disk. Running between that conical disk pair is the endless torque-transmitting means, for example a thrust link belt, a tension chain, or a belt. When the second conical disk is adjusted, the running radius of the endless torque-transmitting means changes, thereby causing the transmission ratio of the continuously adjustable automatic transmission also to change.
Continuously adjustable automatic transmissions require a high level of pressure to be able to adjust the conical disks of the variable speed drive unit at the desired speed at all points of operation, and also to transmit the torque with sufficient baseline contact pressure virtually without any wear.
One of the objects of the invention is to improve power transmission facilitated by a hydraulic medium. Another object of the invention is to simplify the manufacturing of parts and thereby favorably influence manufacturing costs. Another object of the invention is to increase the operational integrity of components and thus extend the life of an automatic transmission of that type. A further object of the invention is to increase the torque transmitting capacity of that type of transmission or to facilitate the transmission of greater power through the components of the transmission.